Stabilized polyketone composition

ABSTRACT

A polymer composition stabilized against degradation during melt processing comprises a major amount of a polymer of carbon monoxide and at least one olefin and a minor amount of a stabilizer. The stabilizer can be a mixture of an aluminum trailalkoxide or hydrolysis product thereof with a amine, preferably a C 12  to C 20  amine; alternatively the stabilizer can be the reaction product of an aluminum alkoxide and an amine, preferably a C 1  to C 20  amine, or it can be a compound of the formula Al(OR x   2 )(NR 3  R 4   y ).

The present invention relates to a stabilised polymer compositioncontaining a polymer of carbon monoxide and one or more olefins. Inparticular the invention relates to compositions containing suchpolymers which exhibit good melt processing stability in processesduring which the composition is melted and subsequently solidified.

The preparation of random copolymers comprised of a minor mount ofcarbon monoxide and a major mount of ethylene by catalysed radicalpolymerisation has been known for some years. More recently it has beenfound that linear alternating polymers of carbon monoxide and one ormore olefins, hereafter called polyketones, can be prepared bycontacting the reactants with a Group VIII metal catalyst preferablycomprised of palladium and a bidentate phosphine, see for example EP121965.

The polyketones prepared by this process, whilst being thermoplastics,suffer from the disadvantage that they have relatively high meltingpoints which are close to the temperatures at which they undergochemical degradation. This causes a problem since the materials are thusdifficult to process using conventional melt technology.

In order to overcome this problem a number of potential approaches havebeen explored. EP 213671 teaches that polyketones comprised of carbonmonoxide, ethylene and alpha olefin (e.g. propylene) units have lowermelting points than corresponding copolymers comprised only of carbonmonoxide and ethylene units. Whilst this approach goes some way toalleviating the problem, there is still a need to improve further themelt processing stability of polyketones if they are to be processed ona commercial scale.

Methods of further improving melt processability have centred around a)the blending of polyketones with other polymers, b) the addition ofplasticisers and c) the use of additives claimed to interfere with thedegradation reactions which the polyketones undergo. The first two typesof approach suffer in that relatively large amounts of the secondpolymer or plasticiser are required, a consequence of which is thatthere is a general deterioration in the physical, mechanical and barrierproperties of the polyketone. An example of the third type of approachis disclosed in EP 310166. This patent teaches the addition of analuminium alkoxide or a derivative thereof. Examples of preferredadditives are those having the general formula Al(OR)₃ where each R isindependently C₁ to C₁₂ alkyl. A disadvantage of this approach is,however, that it has only limited effectiveness. For example, we havefound that whilst there is a stability increase in using up to 2% ofsuch materials with the polyketones, there is no substantial furtherbenefit obtained when higher levels were used.

It has now been found that the melt processability of polyketone blendscontaining an aluminium alkoxide can be improved further by addition ofan additive comprising a C₁₂ to C₂₀ amine.

According to the present invention there is provided a polymercomposition stabilised against degradation during melt processing whichcomprises (a) a major amount of a polymer of carbon monoxide and atleast one olefin, (b) a minor amount of a first stabiliser comprising analuminium trialkoxide or an aluminium containing hydrolysis productthereof and (c) a minor amount of a second stabiliser comprising analiphatic amine, preferably C₁₂ to C₂₀ aliphatic amine.

Furthermore, it has been found that the reaction product obtainable byreacting an aluminium alkoxide with an amine, preferably a C₆ to C₂₀amine can also be used to improve the melt processability ofpolyketones.

According to a further aspect of the present invention there is provideda polymer composition stabilised against degradation during meltprocessing which comprises (a) a major amount of a polymer of carbonmonoxide and at least one olefin and (b) a minor amount of a polymerstabiliser characterised in that the polymer stabiliser is the productobtainable by reacting an aluminium alkoxide with an amine, preferably aC₆ to C₂₀ amine, or an aluminium containing hydrolysis product thereof.

The present invention solves the problem of improving the meltprocessability of polyketones by addition of aluminium/nitrogenstabilisers.

By the term polymer of carbon monoxide and at least one olefin mentionedabove is meant any polymer containing units derived from carbon monoxideon the one hand and units arising from the olefin(s) on the other. Thisdefinition includes both random polymers produced by radicalpolymerisation and the polyketones referred to above. However the use ofthe combination of the stabilisers defined above is particularlyeffective when applied to polyketones. For the purposes of this patent,polyketones are defined as linear polymers having an alternatingstructure of (a) units derived from carbon monoxide and (b) unitsderived from one or more olefins. Suitable olefin units are thosederived from C₂ to C₁₂ alpha-olefins or substituted derivatives thereofor styrene or alkyl substituted derivatives of styrene. It is preferredthat such olefin or olefins are selected from C₂ to C₆ normalalpha-olefins and it is particularily preferred that the olefin unitsare either derived from ethylene or most preferred of all from a mixtureof ethylene and one or more C₃ to C₆ normal alpha-olefin(s) especiallypropylene. In these most preferable materials it is further preferredthat the molar ratio of ethylene units to C₃ to C₆ normal alpha-olefinunits is greater than or equal to 1 most preferably between 2 and 30.

The polyketones described above are suitably prepared by the processesdescribed in EP 121965 or modifications thereof. In general terms, thiscomprises reacting carbon monoxide and the chosen olefin(s) at elevatedtemperature and pressure with a catalyst which is preferably comprisedof palladium, a bidentate phosphine, such asbis(diphenylphosphino)propane, and an anion which either does notcoordinate to the palladium or coordinates only weakly. Example of suchanions include p-toluenesulphonate, tetrafluoroborate, borosalicylateand the like. The process is suitably carried out at a temperature inthe range 50° to 150° C., a pressure in the range 25 to 75 bar gauge andin a solvent such as methanol, acetone, THF or the like.

As regards the case where a first stabiliser (b), an aluminiumtrialkoxide or derivative thereof and a second stabiliser (c) analiphatic amine, preferably a C₁₂ to C₂₀ aliphatic amine are used, thefirst stabiliser is suitably an aluminium alkoxide having the generalformula Al(OR¹)₃ where the R¹ groups are independently C₃ to C₃₆ alkylgroups or substituted derivatives thereof. Preferably the R groups areindependently C₃ to C₁₂ alkyl groups or substituted derivatives thereof.The alkyl groups may contain primary, and/or secondary and/or tertiarycarbon atoms as the case may be.

Most preferred examples of the first stabiliser (b) are compounds havingthe general formula given above where the R groups are identicalsecondary alkyl groups having 3 to 8 carbon atoms. Of these compounds,most preferred of all is aluminium trisisopropoxide. The hydrolysisproducts of aluminium trialkoxides can also be used, e.g. pseudoboehmite.

The amount of aluminium alkoxide used should be in the range 0.1 to 10parts per hundred parts of the composition, preferably 0.3 to 3, mostpreferably 1.0 to 2.0.

Turning to the second stabiliser (c) this can in principle be any aminehaving from twelve to twenty carbon atoms especially those which arealiphatic. Preferred examples are primary aliphatic amines mostpreferably C₁₄ to C₂₀ aliphatic amines, for example, 1-octadecyl amine.The amount of second stabiliser (c) used should preferably be in therange up to 0.5 parts per hundred parts of composition preferably from0.05 to 0.3 parts. It is preferred that the ratio of stabiliser (b) tostabiliser (c) is in the range 20:1 to 0.5:1, preferably about 10:1.

Alternatively, the product obtainable by reacting an aluminium alkoxidewith an amine preferably a C₆ to C₂₀ amine or the aluminium-containinghydrolysis product thereof can also be used as a stabiliser. Suitableexamples of aluminium alkoxides are compounds having the general formulaAl(OR²)₃ where the R² groups are independently C₁ to C₂₀ alkyl, phenylor substituted phenyl. Most preferred are those compounds in which the Rgroups are independently C₁ to C₆ alkyl or phenyl. Particularlyconvenient compounds are those in which the R² groups are C₁ to C₄alkyl.

Turning to the amine, this can be in principle any amine having up totwenty carbon atoms. Especially suitable are aliphatic amines especiallythose which are primary or secondary aliphatic amines having from 6 to20 carbons.

Where the stabiliser is the product obtainable by reacting an aluminiumalkoxide and an amine as described above the stabiliser can be prepared,for example, by reacting the amine and the aluminium derivative togetherin an appropriate inert solvent such as petrol, toluene, xylene, etc.The temperature of reaction will depend upon the exact nature of theamine and aluminium compound used, however, normally a temperature inthe range 0° to 120° C. will be sufficient. Initial mixing of thereactants should preferably be carried out below room temperature.Thereafter the temperature can be raised as appropriate to ensure thatthe reaction goes to completion. An alternative method of preparationinvolves the reaction of an aluminium hydride, alkyl or halide offormula AlX₃ (X=alkyl, Cl, H) with a mixture of the appropriate alcoholand amine.

After reaction is complete the stabiliser can be separated from thesolvent and unreacted starting materials using known techniques such asdistillation.

The reaction product will be of the general formula Al(OR²)_(x) (NR³R⁴)_(y) where x=0, 1-2 and y=3-x where R² is as defined above and thegroup NR³ R⁴ are derivable from a primary or secondary amine, preferablyhaving 6 to 20 carbon atoms, and R³, R⁴ are independently alkyl or arylgroups, preferably alkyl groups, e.g. isopropyl.

Whilst not wishing to be bound by theory, it is believed that thealuminium nitrogen compounds produced by this process are polymericadducts, possibly trimers, of compounds of formula AlX'₃ where the X'groups are independently OR or amino groups derived from the amine byremoval of one of the active hydrogen atoms with at least one X' groupbeing an amino group. In the case where the amine is a primary amine thecompounds may also be polyamine adducts of compounds of formula X₂Al--Y--AlX₂ where the X groups are independently as defined abovewithout the proviso and Y is an amino group derived from a primary amineby removal of both its active hydrogen groups. The process defined abovewill, depending upon the conditions used produce either a pure productof a defined molecular formula or a mixture of such compounds. Both thepure forms and mixtures can be used as stabilisers.

Where the stabiliser is the product obtainable by reacting an aluminiumalkoxide with an amine as described above, the amount of stabiliser tobe used in the polymer composition is typically in the range 0.1 to 10parts per hundred parts of polymer, preferably 0.3 to 3.

The stabilisers can be incorporated into the polyketone by essentiallyany known method provided that intimate mixing is achieved. In thisrespect in the case where two stabilisers (b) and (c) as defined aboveare used, a very convenient method of introducing them is by addition ata temperature above the melting point of the first stabiliser (b). Thusif the first stabiliser (b) is aluminium isopropoxide a temperature inexcess of 118° C., preferably in the range 125° to 180° C. should beused.

Alternatively, the stabilisers can be incorporated by blending finelydivided stabiliser with polyketone powder in a high speed mixer (e.g.Papenmeir Universal High Speed Mixer). In such cases, blending shouldpreferably be carried out with mixing at a speed of 1000 to 2500 rpm.

The improved stability of the composition of the present inventioncompared to the original polyketone manifests itself for example as alower rate of increase in torque at a given temperature when measured ina Brabender torque mixer.

In addition to the components defined above, the composition may containfurther additives such as antioxidants, blowing agents, mould releaseagents and other materials conventional in the art.

The compositions of the present invention may be readily melt processedand hence can be used in the manufacture of containers for food anddrink, automotive parts, wires, cables and structural items for theconstruction industry.

The following Examples now illustrate the invention.

The polyketone used in the following experiments was a terpolymer ofethylene, propylene and carbon monoxide having the followingcharacteristics:

Wt % propylene in polymer: 4.5

Intrinsic Viscosity (dl.g⁻¹): 2.83

Density of powder (g cm⁻³) : 0.273

Comparative Test A

37 gms of the polyketone were charged to a Brabender mixer chamber in<90 seconds and the chamber sealed by a ram supporting a 5 kgm weight.The mixer was driven at 60 rpm and heated by oil circulation to a presettemperature of 230° C.

An initial torque of 22 Nm was observed immediately after sealing whichincreased to 32 Nm after ten minutes. The chamber was opened to reveal asolidified crumb-like material which had clearly crosslinked.

EXAMPLE 1

(according to the Invention)

A blend of polyketone containing 2% AIP and 0.25% octadecylamine wasprepared on the 150 gm scale in a one liter bowl of the Papenmeir atambient temperature and 2500 rpm for 5 minutes. 40 gms of this blend wasnow tested in the Brabender mixing chamber under the same conditions asabove. Initial torque was 22 Nm rising to 24 Nm over 60 minutes.

Comparative Test B

150 gms of the polyketone and 3 gms of aluminium trisisopropoxide (AIP)were blended together at ambient temperature in a Papenmeir UniversalHigh Speed Mixer at 2500 rpm for 5 minutes. 40 gms of this blend wascharged to the Brabender mixer chamber and tested under the sameconditions as in the previous example. The initial torque was 21 Nm andincreased slowly to 23 Nm over a period of 60 minutes at which time itwas just beginning to show signs of becoming a crumb.

Comparative Test C

About 40 gms of the blend of Comparative Test B was prepared in two lotsof 20 gms by preblending at 30 rpm in a Brabender mixing head heated to150° C. The powder obtained now was a buff colour. The standardBrabender test was performed at 230° C. as in the previous examples. Theinitial torque was now lower at 17 Nm than observed when mixing wascarried out at ambient (22 Nm) and rose to only 19 Nm. Stability timewas now only 50 minutes (taken as the time to peak torque at which onsetof crosslinking is anticipated).

EXAMPLE 2

(according to the Invention)

A further 40 gms of the blend prepared in Example 1 was further mixed inthe Brabender chamber (in two batches of 20 gms) for five minutes at 30rpm at 125° C. Subsequently, the blend was subjected to the Brabendertest and gave a stability time of 66 minutes and a torque rise from 22Nm to 25 Nm.

EXAMPLE 3

(according to the Invention)

A further 40 gms of the blend prepared in Example 1 was similarlyfurther mixed in the Brabender in two batches of 20 gms at 150° C. and30 rpm. In a subsequent Brabender test at 230° C. and 60 rpm, theinitial torque registered was reduced to 12 Nm initially rising to 16 Nmafter sixty minutes.

The comparative tests and Examples show that a subsequent mixingprocedure in which the blend is held at 150° C. causes 8-10 Nm drop intorque over the whole test period. This may be due to better dispersionof the octadecylamine and possibly also the AIP resulting from the factthat they become molten in this temperature range.

EXAMPLE 4 AND 5

(according to the Invention)

In these tests 2% AIP and 1% octadecylamine were employed. In Example 4the blend was prepared at ambient temperature in the Papenmeir and theinitial and final Brabender torques were 20 and 21 Nm after 60 minutes.In Example 5 employing an additional mixing procedure at 150° C. theinitial and final torques were 20 and 23 Nm (after 53 mins).

The invention clearly establishes that there is a synergisticinteraction between stabiliser and lubricant which is enhanced by mixingabove their melt temperatures.

The use of reaction products from the reaction of aluminium trialkoxideswith amines as stabilisers is described below.

EXAMPLE 6

(according to the Invention)

A. Preparation of the Stabiliser-Reaction Product of Aluminiumtrisisopropoxide and 1-Octadecylamine

Aluminium trisisopropoxide (21.7 g, 0.1M) was dissolved in anhydroustoluene (100 ml). 1-Octadecylamine (28.7 g, 0.1M) as a slurry withtoluene (100 ml) was added dropwise to this solution at 0° C. Themixture was allowed to warm to 25° C. and stirred at 25° C. for 4 hours.The solution was homogeneous by this time. Toluene/isopropanol was thenremoved by distillation in vacuo at 40° C. followed by pumping underhigh vacuum at 100° C. to give a waxy solid.

Aluminium content 6.3% w/w For (C₁₈ H₃₇ NHAl(OCH(CH₃)₂)₂)_(n) Al=6.5%.Found C, 69.9%; H, 12.1%; N, 3.6% Calculated for (C₁₈ H₃₇NHAl(OCH(CH₃)₂)₂)_(n) C, 69.7%; H, 12.7%; N, 3.4%. 13C NMR spectroscopyindicated that the product contained less than 10% by weight ofaluminium trisisopropoxide.

B. Use of the Stabiliser

General Procedure

Polyketone (ethylene-propylene-carbon monoxide) terpolymer was processedon a Brabender Plasticorder, a laboratory batch melt mixer, and thetorque on the rotors and the melt temperature were monitored over 30minutes. On addition of polymer to the mixer the torque rises as thepolymer fuses then drops within a few minutes as the polymer melts andthe temperature equilibriates and reaches a minimum value. Increase intorque with time beyond this minimum is indicative of increasingviscosity due to crosslinking. Also as the viscosity increases, the melttemperature increases due to the heat of working. A stabilising effectwould be manifested as a reduction in the rate of torque increase andmelt temperature increase. The mixing was carried out with a rotor speedof 60 rpm and an initial temperature of 215°±2° C. under a nitrogenatmosphere, achieved by a flow of nitrogen passing around the rotorshaft and also over the top of the ram. The stabiliser was crushed to apowder and mixed using a spatula with the polymer powder in a beakerprior to processing. 36 g of polymer were charged to the mixing chamberin each run.

The melt flow rate (MFR) of the polymer was measured using a DavenportMelt Index Tester at 240° C. under either a 5 kg or a 21.6 kg load. Themelt flow rate was taken as the 30 second flow 3 minutes after chargingthe material into the barrel of the instrument at temperature. Otherwisestandard procedures were followed (ASTM D 1238-86). A decrease in MFRafter processing a given material is indicative of increased viscositydue to crosslinking reactions. A stablising effect is evidenced byprotection of/limitation of such a melt flow ratio drop.

B1. Two batches of polyketone powder, one having intrinsic viscosity(measured at 30° C. in m-cresol) of 1.40 dlg⁻¹ and melting point 200° C.(the peak of the endotherm measured by DSC scanning at 10° C. min⁻¹) andthe other having intrinsic viscosity 1.45 dlg⁻¹ and melting point 201°C., were dry blended by mechanical shaking. The melt flow rate of thepowder mixture was 41 g/10 min at 240° C. and 5 kg. Details ofprocessing response with and without the product of Example 6 Al beingpresent are given below.

    ______________________________________                                        Brabender Processing Response                                                                         Resultant                                             Stabilizer                                                                            Minimum  Final    Final   Melt Flow Rate                              Loading Torque   Torque   Melt Temp.                                                                            @ 5 kg, 240° C.                      (pph)   (gm)     (gm)     (°C.)                                                                          (g/10 min)                                  ______________________________________                                        0       730      1270     233     no flow                                     2       780       970     225     7.2                                         ______________________________________                                    

B2. Two batches of polyketone powder, one having an intrinsic viscosityof 1.52 dlg⁻¹ and melting point 195° C. and the other having anintrinsic viscosity of 1.49 dlg⁻¹ and melting point 202° C., were dryblended by mechanical agitation/shaking. The melt flow rate of thepowder mixture was 28 g/10 min at 240° C. and 5 kg. Details of theprocessing response with and without the product of Example 6 Al beingpresent are given below.

    ______________________________________                                        Brabender Processing Response                                                                         Resultant                                             Stabilizer                                                                            Minimum  Final    Final   Melt Flow Rate                              Loading Torque   Torque   Melt Temp.                                                                            @ 5 kg, 240° C.                      (pph)   (gm)     (gm)     (°C.)                                                                          (g/10 min)                                  ______________________________________                                        0       790      1390     245     no flow                                     1       780       990     226     6.3                                         ______________________________________                                    

B3. A single batch of polyketone with intrinsic viscosity of 2.1 dlg⁻¹and melting point 215° C. was used. Details of the processing responsewith and without the product of Example 6 Al being present are givenbelow. The melt flow rate of the powder prior to processing was 26 g/10min at 240° C. and 21.6 kg.

    ______________________________________                                        Brabender Processing Response                                                                         Resultant                                             Stabilizer                                                                            Minimum  Final    Final   Melt Flow Rate                              Loading Torque   Torque   Melt Temp.                                                                            @ 5 kg, 240° C.                      (pph)   (gm)     (gm)     (°C.)                                                                          (g/10 min)                                  ______________________________________                                        0       1700     265       250*   no flow                                     1       1590     2450     265     0.9                                         ______________________________________                                         *after 6 minutes  whereas the sample with the stabiliser was processed fo     30 minutes.                                                              

EXAMPLE 7

The following compounds:

(a) tris(diisopropylamino) aluminium

(b) di(isopropoxy) (diisopropylamino) aluminium

(c) isopropoxy bis(diisopropylamino) aluminium

(d) tris(dodecylamino) aluminium were prepared.

(a) and (d) were prepared by the method of J K Ruff (J. Amer. Chem. Soc.1961, 83 2835); (a) was then further reacted with 1 and 2 equivalents ofisopropanol to give (c) and (b) respectively.

The above compounds were then incorporated into a polyketone and testedas described below.

A polyketone with intrinsic viscosity (measured at 30° C. in m-cresol)of 1.55 d/g⁻¹, melting point (peak of DSC endotherm on scanning at 10°C./min.). 200° C. and melt flow rate (240° C., 5 kg) of 20 g/10 min. wasmixed with stabilising additives as described below. Details of theprocessing response with and without stabiliser are given in Table I.

Incorporation of Additives into Polymer

Polyketone powder was added to a glass flask and was subsequently driedat 70° C. under vacuum for several hours. Under dry, inert conditionsthe required amount of stabiliser was dissolved in dry toluene. Thissolution was then added to the dry polymer powder in the glass flaskunder inert conditions. The powder was slurried with the solution andthe toluene was subsequently removed by vacuum distillation leaving thestabiliser impregnated on the polymer powder. The polymer/stabilisermixture was stored under dry, inert conditions.

Polymer Processing Evaluation

The polymer was processed as described in Example 6B except that themixing was carried out at an initial temperature of 212°±2° C.

                  TABLE I                                                         ______________________________________                                                                  Resultant                                                                     Melt                                                         Brabender Processing Response                                                                  Flow Rate                                                 Stabiliser                                                                             Minimum  Final Final   @ 240° C.                        Sta-  Level    Torque   Torque                                                                              Melt Temp.                                                                            (g/10 min.)                             biliser                                                                             (pph)    (Nm)     (Nm)  (°C.)                                                                          5 kg 21.6 kg                            ______________________________________                                        None  --       6.8      16.0  240     no   no                                                                       flow flow                               a     1.0      8.7      12.3  235     2.2  33                                 b     1.0      12.1     13.1  227     1.8  31                                 c     1.0      9.5      14.1  235     0.7  13                                 d     1.0      8.6      17.8  250     no   1.7                                                                      flow                                    ______________________________________                                    

We claim:
 1. A polymer composition stabilized against degradation during melt processing which comprises (a) a major amount of a polymer of carbon monoxide and at least one olefin; (b) a minor amount of a first stabilizer comprising an aluminum trialkoxide or an aluminum containing hydrolysis product thereof and (c) an amount in the range 0.05 to 3% by weight of the composition of a second stabilizer comprising an aliphatic mono-amine containing from 12 to 20 carbon atoms.
 2. A polymer composition as claimed in claim 1 wherein the first stabiliser is aluminium tris(isopropoxide) or an aluminium containing hydrolysis product thereof.
 3. A polymer composition as claimed in claim 1 wherein the first stabiliser is present in an amount in the range 1 to 2% by weight of the composition.
 4. A polymer composition as claimed in claim 1 wherein the first and second stabilisers are incorporated into the polyketone by addition of said first and second stabilisers at a temperature above the melting point of the first stabiliser.
 5. A polymer composition as claimed in claim 1 or claim 2 wherein the amine is 1-octadecylamine.
 6. A polymer composition stabilized against degradation during melt processing which comprises (a) a major amount of a polymer of carbon monoxide and at least one olefin; (b) a minor amount of a first stabiliser comprising an aluminum trialkoxide or an aluminum containing hydrolysis product thereof; and (c) an amount in the range of 0.05 to 3% by weight of the composition of 1-octadecylamine.
 7. A polymer composition stabilized against degradation during melt processing which comprises (a) a major amount of a polymer of carbon monoxide and at least one olefin, and (b) a minor amount of polymer stabilizer characterized in that the polymer stabilizer is the product obtainable by reacting at a temperature of 0° to 120° C. equal molar proportions of an aluminum alkoxide or an aluminum containing hydrolysis product thereof with a primary or secondary aliphatic mono-amine having up to 20 carbon atoms.
 8. A polymer composition as claimed in claim 7 wherein the aluminum alkoxide is of the general formula a Al(OR²)₃ where R² is a C₁ to C₂₀ alkyl, phenyl or substituted phenyl.
 9. A polymer composition as claimed in claim 8 wherein R is a C₁ to C₄ alkyl group.
 10. A polymer composition stabilized against degradation during melt processing which comprises (a) a major amount of a polymer of a carbon monoxide and at least one olefin and (b) a minor amount of a polymer stabilizer which is a compound of the formula Al(OR²)_(x) (NR³ R₄)_(y) where x is 0 or 1-2, y is 3-x, and R² is a C₁ to C₂₀ alkyl, phenyl or substituted phenyl group and the group NR³ R⁴ is derivable from a primary or secondary mono-amine, R³ and R⁴ are independently alkyl or aryl groups.
 11. A polymer composition as claimed in claim 10 wherein the group NR³ R⁴ is derivable from a primary or secondary amine having 6 to 20 carbon atoms.
 12. A polymer composition as claimed in claim 7, claim 8, claim 9, claim 10 or claim 11, wherein the amount of (b) the polymer stabiliser is in the range 0.1 to 10% by weight of the composition.
 13. A polymer composition as claimed in claim 12 wherein the amount of (b) the polymer stabiliser is in the range 0.3 to 3% by weight of the composition. 